The present invention relates to a waterproofing membrane based on bitumen modified with polyolefins which can be applied on-site by using oxidized or air-blown bitumen.
As is well-known to the experts in the field, bitumen is generally modified by using polymers in order to produce mixtures which, when hot, are suitable for impregnating and coating supporting frames of various kinds for coverings, in order to obtain membranes which can ensure the waterproofing of the coverings of buildings and structures in general.
A distinction is often made between membranes based on bitumen modified with elastomers and those based on bitumen modified with polymer plastics. In the former, the waterproofing mass is essentially constituted by a mixture of bitumen and elastomers of the SBS (styrene-butadiene-styrene) block copolymer type, whereas in the latter if is constituted by mixtures of thermoplastic polyolefins and distilled bitumens. The most used polyolefins are atactic polypropylene, a by-product which is generally obtained from the production of isotactic polypropylene, and the ethylene-propylene copolymer, which also has an amorphous nature.
Waterproofing membranes are generally obtained in sheets of 3,4 or 5 mm thickness and, if total or partial adhesion to the support is required, they can be applied either by means of a propane-gas torch, which by liquefying the bituminous mass makes it adhere to said support, or by using hot air-blown bitumen which acts as an adhesive.
However, while membranes based on bitumen modified with SBS yield good results with both methods (with preference for the air-blown bitumen method, due to some limitations of the SBS membrane with the torch method, such as excessive softening which almost always prevents rapid and easy application of the membrane, especially in summer), polyolefin-based membranes generally yield the best results only with the flame method; this especially because otherwise, in the course of time, adhesion tends to decrease due to the forming of an oily layer between the air-blown bitumen and the membrane which causes its separation in the course of time.
This fact constitutes a limitation to the use of polyolefin-based membranes (especially in some countries, where the use of hot bitumen is still very common), which instead intrinsically have, with respect to membranes based on SBS elastomer, some distinct advantages, such as greater resistance to aging (both thermal aging and aging due to the action of UV rays) and a better seal at high temperatures.
It is also well-known to add, as already mentioned, polyolefins to the bitumen, and to use polyolefins together with their copolymers and rubbers Generally, these products are added in order to improve some mechanical characteristics of the mixtures, such as flexibility at low temperatures, elasticity or ultimate elongation.
This is taught for example by U.S. Pat. No. 4,659,759, in which an elastomeric component (an ethylene-propylene copolymer) is added to the bitumen in order to improve its properties at high and low temperatures. European patent no. 0009432 provides for the addition of SBS (styrene-butadiene-styrene) to a mixture of bitumen +polyolefins in order to improve its characteristics in terms of resistance to low temperatures as well as the ultimate elongation of the mixture.
From this point of view, an exception is found in U.S. Pat. No. 4,771,090, which provides for the use of an amorphous copolymer of ethylene-propylene-butadiene (EPDM) in order to obtain a waterproofing membrane which can be flame-applied onto a previous waterproofing layer produced with material based on air-blown bitumen.
However, said patent expressly states that the presence of a particular EPDM elastomer in the composition of the waterproofing mass is indispensable in order to achieve good adhesion to the product based on air-blown bitumen; as is known, this is a relatively very expensive elastomer. All this is supported by numerous examples which demonstrate the validity of this statement